Tunisia votes on Sunday in its first ever free elections, the first vote of the Arab spring. But the mood of optimism is tempered with deep unease that, nine months after the revolution which ousted the dictator Zine El Abidine Ben Ali, the country is still dominated by the corrupt and brutal vestiges of the old regime.

Voting is to elect an assembly with one specific mission: to draw up a new constitution before parliamentary elections scheduled to take place within 12 months. The Islamist party An-Nadha, which was outlawed and brutally repressed by the Ben Ali regime, is expected to take the biggest share of the vote, and says it will defend democracy and women's rights. But the complex proportional representation system means that, no matter how the votes are cast, no one party will have a majority or be able to dominate.

On the street Tunisians, fiercely proud that their uprising launched the Arab spring, warned that the most pressing issue was safeguarding their "unfinished revolution."

Lawyers complain that police brutality and torture continues in the small north African country, which under Ben Ali was notorious as having the most pervasive secret police in the region. Human rights activists say Ben Ali's cronies and former party sympathisers still dominate a crooked justice system, that corruption has worsened, and that notorious servants of the old regime have even been promoted since the revolution. Some describe a climate of impunity, symbolized by Ben Ali's flight to Saudi Arabia, where he can avoid facing trail for his crimes. Meanwhile, in Tunisia, his influence continues to pervade officialdom and the workings of the state.

"We are overwhelmed with cases of human rights abuses. You wouldn't believe there had been a revolution," said Imene Triki, a human rights activist. "Torture is the way things are done, it's systematic. They have not changed their practices at all," she said, warning of "countless" cases in police stations and prisons.

She described: the "systematic and routine" arrests of bloggers and activists on fabricated charges, often of "burning police stations"; arrests of people labelled "Salafists" who were out of the country at the time their alleged crimes were committed; and the arrests of children.

Triki described one case, of an alleged robber who was transferred to hospital from prison with a stomach complaint. While in hospital, she claims, he was brutally beaten and sexually assaulted in front of the doctors, nurses and other patients. Triki says she found him with his legs chained to the bed and severe injuries to his genitals and that in the same hospital she found another prisoner lying in the emergency ward, his body festering with worms and covered in excrement. He had, she says, been there for a month.

Ahmed Rahmouni, head of the Association of Tunisian Magistrates, described a rotten justice system - still in place – in which judges were used by Ben Ali as a "tool of repression" to crack down on civil society. Although some judges were independent, he said, the overwhelming system remained in thrall to politicians and dominated by those who served Ben Ali. These judges continue to try cases. "The country's top judges are corrupt, inefficient and an instrument of dictatorship. We need to get rid of them, and restore trust in the judiciary," he said.

Sihem Bensedrine, a human rights activist and head of Kalima radio station, has returned from exile but has still not been issued with a licence for her radio station, which broadcasts online. She said: "The revolution cut off the head, but the body is still there. Dictatorships aren't just about security per se - they are also about the security forces controlling the media, culture, health care, universities, hospitals. You need to dismantle the whole machine. There are three elements: the secret police, the old guard of the former ruling party and the businessmen corrupted by working with the regime. These three are still powerful, they still have long arms."

After nine months of discredited and weak interim governments featuring ageing faces from Tunisia's recent past, Tunisians insist that the old guard must be rooted out of officialdom and daily life, and that this must be coupled with quick answers to the country's major problem, unemployment, a central cause of the revolution. Officially at 19%, unemployment has soared since January, but most believe the real figures are far higher. The jobless rate for graduate women is over 40%. In the poorer interior of the country the figures are double the national rate.

Lina Ben Mhenni, a blogger who was nominated for this year's Nobel peace prize, warned that Tunisia was being held back by the old regime and "after a few weeks of revolutionary euphoria" the country once again risked turning into a police state with the regime's apparatus still in place. Disillusioned at the ongoing presence of the old regime, she said she wouldn't vote.

In purely political terms, Ben Ali's ruling RCD party has been dissolved and its figureheads are forbidden from standing for election. But in a bewildering political landscape of over 110 new parties and scores of independent candidates, several small, marginal new parties have regrouped supporters from the old RCD. They aim to win over a dozen seats between them.

In the offices of one new party, Al-Watan, the Nation or Homeland, its leader Mohamed Jegham said there was a prevailing current in Tunisia since the revolution "and we can't go against the current". But Jegham, a one-time interior minister and defence minister of Ben Ali, said he was proud of what he called the good state infrastructure left behind by the Ben Ali era and said the country "needs people who know the terrain". He was critical of the removal of regional governors linked to the regime.

Formerly minister in charge of police, he said: "The police needs to go back to being in the service of the country, of the nation, and not just in the service of the president or ministers. Not all officers can do that. There will be change - some have left, some are more reticent - the majority can do it." He said corruption must be stopped but that it would not be easy. "We need new laws and for those to be respected."

Saida Lakrimi, of the Tunisian lawyers union, said: "We are in a transitional period, but the pace is very, very slow. Changes to institutions need to happen more quickly to cleanse the system … Popular discontent will fester if those who robbed and killed and tortured are not tried in a fair and transparent way … You can't create the future using the tools of the past."

Journalists' organisations complained that even the media, which was so tightly censored under Ben Ali that even the airbrushed photographs of the great man were chosen and provided by his office, was yet to be overhauled.

Kamel Labiti, head of the commission for media reform, said the media landscape had not changed. Media owners still had connections in the administration, and undue influence.

"We have a culture of praising the king. You can't change that in a few months," he said, also citing a lack of training for journalists. He said that "for decades journalists have effectively been civil servants."

Najiba Hamrouni of the journalists union said: "Since the revolution we have greater freedom in terms of what we can cover in the mainstream press, who we can interview and so on. However, the problem is that the main media organisations are controlled and run by the same Ben Ali men, and they are censoring their journalists. Managers dictate editorial policy. Some people and issues are marginalised." New press titles have launched but many have folded through lack of funds.

On the streets of central Tunis, most people were optimistic that the elections could mark the beginning of the end of the unfinished revolution. But people were vigilant. Many vowed that if they sensed anything but total transparency and fair elections, they would once again take to the street.

Rhamouni said he saw a new "dynamism and plurality in Tunisian society", which gave him hope. "Tunisian people believe they started the first revolution in the Arab world. They won't accept the manipulation of their will. It is not just the elite who are talking about the need to cleanse the judiciary, but ordinary people. There is an unprecedented state of awareness in the country."